Just testing the Ze at origin on a TT system which was 256 ohms. The PSC is 1.1KA, 0.22 ohms. The PEFC is 1A. I was expecting the PEFC to be a lot higher and Ze a lot lower. The main earthing cable is unprotected coming straight from the floor. The system has a Residual Current Operated Circuit Breaker 100ma trip. Please advice on next course of action (in the process of rewiring the house) no experience on TT systems!

50v touch voltage... 50v/0.1mA=500ohm
If the spike is 256 under worst conditions the RCD will be ok to protect for fault as far as the CU. But you should really fit a plastic enclosure 100mA(s) type or same spec as CU main switch with the rest of the installation split between two 30mA RCD and possibly smoke detectors on it's own RCBO.
That's what I would do!

Originally posted by: luggseyBut you should really fit a plastic enclosure 100mA(s) type or same spec as CU main switch with the rest of the installation split between two 30mA RCD and possibly smoke detectors on it's own RCBO.
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If a dual 30mA RCD CU is fitted then why would you need a 100mA RCD upstream, all circuits are 30mA protected and overall isolation is via the DP switch in the CU.

A lot of older TT installs have a seperate RCD, so the tails are fault protected.
The mains board 'should' have reinforced insulation on the busbars if you fit a main switch only as there is no fault protection to them, you are also limited to a class2 plastic CU this way.
Easier to fit an RCD(s) main switch IMO.

I'd be very tempted to check out the condition of the elcetrode outside. would have thought you should be lower than 256 ohms with a decent electrode. Theoretical max for a 100mA RCD is 500 ohms but regs suggests 200 max.